Prior art devices designed to activate an acoustic signal, a canopy opening mechanism or other operators are all based on the principle of activating the device when a certain barometric air pressure and/or air speed has occurred or after a preset elapsed time after a mechanical or electrical chronometer has been activated manually, see e.g. EP 48 07 33 and US 47 83 027.
None of the prior art devices are able to determine the exit time automatically, which could otherwise enhance the safe function of such devices and further contribute to presenting better information, preferably audible, to the parachutist when descending.